A flavan compound such as a proanthocyanidin and catechins is a polyoxy derivative (flavanonol) having a flavan skeleton, or polymer thereof, and classified as a condensed tannin group. From a long time ago, a flavan compound has been used industrially for leather tanning, and in cosmetics in order to provide a skin conditioning effect by improving astringency of the skin, for example. Recently, a flavan compound has been used in foods, cosmetics, and the like, because of its various activities such as an antioxidation properties and a whitening effect (Japanese Laid-Open Patent Publication No. S61-16982 and Japanese Laid-Open Patent Publication No. H2-134309). For example, a cosmetic article is known in which a protein (e.g., collagen) such as a collagen is blended with a flavan compound such as proanthocyanidin (Japanese Laid-Open Patent Publication No. H11-75708, Japanese Laid-Open Patent Publication No. 2000-60482, Japanese Laid-Open Patent Publication No. H6-336423, and Japanese Laid-Open Patent Publication No. 2002-238497).
However, a flavan compound has an extremely high ability to bind to a protein. Thus, when a flavan compound is extracted from a plant, it may be bound to a protein also included, so as to cause coagulation-precipitation, suspension, gelatinization, or the like, depending on factors such as the type of the plant and the method of extraction.
Recently, a flavan compound such as a proanthocyanidin has been used for producing gelatin gel having a high melting point or as a crosslinking agent of collagen, utilizing its high ability to bind to protein (Japanese Laid-Open Patent Publication No. H2-163046 and Japanese Laid-Open Patent Publication No. 2001-8634). However, usually, a flavan compound may causes a problem due to this ability in foods, drugs, quasi-drugs, cosmetics, and the like.
For example, once a flavan compound is coagulated and precipitated, or gelled with protein in a solution during the manufacturing process, a proanthocyanidin or protein must be degraded by treatments such as an acid treatment or an alkali treatment in order to dissolve them again. Thus, it is difficult to produce articles such as foods, drugs, quasi-drugs, and cosmetics containing these components. Furthermore, even if these articles can be produced, there is a problem that coagulation-precipitation may be caused during a storage period in a case of formulated in a liquid preparation such as beverage or skin lotion.
In order to address these problems, Japanese Laid-Open Patent Publication No. 2002-51734 has disclosed an improved method for enhancing the stabilities of tannin, which is a flavan compound, and collagen, which is protein, in a solution. However, this method has a problem that collagen used is limited to low molecular weight collagen peptides.